1. Field of the Invention
The present invention relates to the art of earth boring. In particular, the invention relates to methods and apparatus for remotely controlling the operation of downhole tools.
2. Description of Related Art
In pursuit of deeply deposited economic minerals and fluids such as hydrocarbons, the art of earthboring involves many physical operations that are carried out remotely under hazardous and sometimes hostile conditions. For example, hydrocarbon producing boreholes may be more than. 25,000 ft. deep and have a bottom-hole pressure more than 10,000 psi and a bottom-hole temperature in excess of 300 F.
Transmitting power and control signals to dynamic tools working near the wellbore bottom is an engineering challenge. Some tools and circumstances allow the internal flow bore of a pipe or tubing string to be pressurized with water or other well working fluid. Sustained high pressure may be used to displace sleeves or piston elements within the work string. In other circumstances, a pumped circulation flow of working fluid along the pipe bore may be used to drive a downhole fluid motor or electric generator.
The transmission of operational commands to downhole machinery by coded sequences of pressure pulses carried along the wellbore fluid has been used to signal the beginning or ending of an operation that is mechanically executed by battery power such as the opening or closing of a valve. Also known to the prior art is the technique of using in situ wellbore pressure to power the operation of a mechanical element such a well packer or slip.
All of these prior art power and signal devices are useful in particular environments and applications. However, the challenges of deepwell drilling are many and diverse. New tools, procedures and downhole conditions evolve rapidly. Consequently, practitioners of the art constantly search for new and better devices and procedures to power or activate a downhole mechanism.
“Controllable fluids” are materials that respond to an applied electric or magnetic field with a change in their rheological behavior. Typically, this change is manifested when the fluids are sheared by the development of a yield stress that is more or less proportional to the magnitude of the applied field. These materials are commonly referred to as electrorheological (ER) or magnetorheological (MR) fluids. Interest in controllable fluids derives from their ability to provide simple, quiet, rapid-response interfaces between electronic controls and mechanical systems. Controllable fluids have the potential to radically change the way electromechanical devices are designed and operated.
MR fluids are non-colloidal suspensions of polarizable particles having a size on the order of a few microns. Typical carrier fluids for magnetically responsive particles include hydrocarbon oil, silicon oil and water. The particulates in the carrier fluid may represent 25-45% of the total mixture volume. Such fluids respond to an applied magnetic field with a change in rheological behavior. Polarization induced in the suspended particles by application of an external field causes the particles to form columnar structures parallel to the applied field. These chain-like structures restrict the motion of the fluid, thereby increasing the viscous characteristics of the suspension.
ER systems also are non-colloidal suspensions of polarizable particles having a size on the order of a few microns. However, with applied power, some of these fluids have a volume expansion of 100%. Some formulations, properties and characteristics of controllable fluids have been provided by the authors Mark R. Jolly, Jonathan W. Bender and J. David Carlson in their publication titled Properties and Application of Commercial Magnetorheological Fluids, SPIE 5th Annual Int. Symposium on Smart Structures and Materials, San Diego, Calif., March, 1998, the body of which is incorporated herein by reference.
It is, therefore, an object of the present invention to provide a new downhole operational tool in the form of electrically responsive polymers as active tool operation and control elements.
Also an object of the present invention is the provision of a downhole well tool having no moving fluid control elements.
Another object of the present invention is a disappearing flow bore plug that is electrically ejected from a flow obstruction position.